Multifocal lens

ABSTRACT

The invention relates to a multifocal lens ( 1 ) with a refractive focus (F r ) and with a diffractive structure ( 5 ) which, in the radial direction (r) of the lens ( 1 ), plotted across the squared radius (r 2 ), has a periodic profile ( 6, 7, 8, 9 ), wherein the profile ( 6, 7, 8, 9 ) per period has four adjoining portions ( 6, 7, 8, 9 ) which are not differentiable at their connection sites ( 10, 11, 12, 13 ), wherein a first portion ( 9 ) has a monotonically falling function and the three further portions ( 6, 7, 8 ) have a monotonically rising function or vice versa, and wherein the further portion ( 7 ), which does not adjoin the first portion ( 9 ), has a greater pitch than the other further portions ( 6, 8 ).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/765,078, filed Mar. 30, 2018, which is a National Phase ofPCT/EP2016/073361, filed Sep. 29, 2016, which claims priority toEuropean Patent Application No. 15188045.7, filed Oct. 2, 2015, thedisclosures of each of which are incorporated herein by reference.

FIELD OF THE DISCLOSURE

The present invention relates to a multifocal lens with a refractivefocal point and a diffractive structure, the structure having a periodicprofile in the radial direction of the lens plotted over the squaredradius, and the profile having four mutually adjacent portions perperiod which cannot be differentiated at their junctions.

BACKGROUND OF THE DISCLOSURE

Multifocal intraocular or contact lenses, i.e. lenses with a pluralityof focal points, which may for example be used for near and distancevision (bifocal) or near, intermediate and distance vision (trifocal),have been known for several decades and use a very wide range ofdiffractive structures on a refractive basic lens, in order to provideone or more diffractive focal points in addition to the refractive focalpoint.

According to documents DE 20 2009 018 881 U1 and EP 2 503 962 B1, toproduce two diffractive focal points lenses with diffractive structuresare used, the profile of which per period has four alternatelymonotonically rising and monotonically falling portions, i.e. twoacute-angled maxima per period. The applicant has recognised thatincorporating such structures into the lens not only leads to aplurality of profile peaks which are difficult to manufacture, but alsoto suboptimal distribution or light yield of the light intensities inthe focal points produced.

SUMMARY OF THE DISCLOSURE

The object of the invention is to provide an improved lens whichovercomes the disadvantages of the prior art.

According to the invention, the object is achieved with a lens of theabove-stated type in which a first portion of the profile fallsmonotonically and the three further portions rise monotonically, or afirst portion rises monotonically and the three further portions fallmonotonically, and wherein the further portion which does not adjoinsaid first portion has a steeper gradient than the other two furtherportions.

With the structure according to the invention, a lens is provided whosefocal points usable for near, intermediate and distance vision have ahigher intensity component than is known in the prior art. For moreprecise consideration of the problem, “positive” order diffractive focalpoints will hereinafter be defined as those which are located betweenthe lens and its refractive focal point, and “negative” orderdiffractive focal points as those which are located on the side of therefractive focal point remote from the lens.

If the refractive focal point is used for distance vision, for example,the first positive order focal point of the diffractive structurecorresponds to a distance for intermediate vision and the secondpositive order focal point of the diffractive structure to a distancefor near vision. The respective negative focal points of the diffractivestructure will in this case form an image only behind the lens user'sretina, for which reason they are not useful to the user and contributeto an impairment of image quality.

In the case of the lens according to the invention, in contrast,intensity components of the (originally) negative orders are imaged ontothe positive orders used or onto the zeroth (refractive) order,resulting in a more intensely coloured, higher contrast image comparedto the prior art, since the useful focal points comprise higherintensity components.

The same advantages are obtained if, for example in an alternativeembodiment, the refractive focal point is used for near vision, and thefirst negative order focal point of the diffractive structurecorresponds to a distance for intermediate vision and the secondnegative order focal point of the diffractive structure corresponds to adistance for distance vision. In this embodiment, the positive orders ofthe diffractive structures are of little use, since they are located infront of the near vision focal point, and the third negative orderorders are of no use at all, since they are only focused behind theretina. According to the invention, intensity components of the positiveorders are here imaged onto the zeroth (refractive) negative first andnegative second order, again resulting in a higher light yield in theuseful focal points and thus a more intensely coloured, higher contrastimage compared to the prior art.

In each embodiment, the lens according to the invention lensadditionally has the significant advantage that the diffractivestructure of the lens comprises just one maximum per period andnonetheless produces two diffractive focal points. Production of thediffractive structure on the lens may thus proceed far more simply andwith less waste, since the angle of the maximum is larger and moreoveronly occurs once per period, i.e. only half as often as with thediffractive structures according to the prior art, which produce twodiffractive focal points. Higher lens accuracy may be achieved inparticular at the periphery of the lens, at which the period lengths maybe very small, due to the more precise manufacture made possiblethereby, leading in turn to more precise, more controlled lightdistribution.

The refractive focal point of the lens may, as discussed, be used eitherfor near vision or distance vision. If the refractive focal point isused for distance vision, the preferred embodiment is the one in whichthe first portion falls monotonically and the three further portionsrise monotonically. Alternatively, the refractive focal point may beused for near vision, wherein the first portion then preferably risesmonotonically and the three further portions fall monotonically.

The portions, plotted over the squared radius, are preferably linear,i.e. they result in quadratically rising or falling flanks on the lens.This allows a simple calculation of the intensity profile of the lens.Alternatively, the portions may also comprise individual profiles, inorder to adapt the intensity distribution of the lens.

In one preferred embodiment, the stated first portion is substantiallyvertical. Irrespective thereof, the further portion which does notadjoin the first portion may also be substantially vertical. These twomeasures result in an extremely simple profile pattern, since then onlythe gradient of two portions remains to be determined. This alsosimplifies manufacture of the lens, because a vertical portion, plottedover the squared radius, also results in a vertical flank on the lens.

To simplify calculation of the profile and consequently also manufactureof the lens, the two further portions which each adjoin the firstportion, plotted over the squared radius, may have substantially thesame gradient.

In one practical embodiment, two further portions which each adjoin thefirst portion, plotted over the squared radius, have a gradient of 1μm/mm² to 10 μm/mm². Furthermore, the period of the profile, plottedover the squared radius, preferably amounts to 0.5 mm² to 1 mm² and theprofile depth to 2 μm to 10 μm. This yields a lens whose focal pointsfor near and intermediate vision lie at distances desired by users.

BRIEF DESCRIPTION OF THE FIGURES

The invention is explained in greater detail below on the basis ofexemplary embodiments shown in the appended drawings, in which:

FIG. 1 is a schematic plan view of the lens according to the invention;

FIG. 2 is a schematic side view of the lens of FIG. 1;

FIG. 3 shows an enlarged half section of the lens of FIG. 1;

FIG. 4 shows the profile of the diffractive structure of the lens ofFIGS. 1-3, plotted over the squared radius of the lens; and

FIG. 5 shows a comparison of the intensity distribution of the lensaccording to the invention with that of a lens according to the priorart.

DETAILED DESCRIPTION OF THE DISCLOSURE

FIGS. 1 and 2 show a lens 1 with a front face 2, a back face 3 and anoptical axis 4. The lens 1 has a central zone Z₁ and an annular zone Z₂,which are explained in further detail below. The described lens 1 isused in particular as an intraocular lens or contact lens, but may alsobe used in optical equipment.

The lens 1 has a refractive focal point F_(r) located on the opticalaxis 4, which focal point may be used, as described below, for distanceor near vision and is also described hereinafter as a zeroth order focalpoint. A diffractive structure 5 is incorporated into the back or front2, 3 of the lens 1, see FIGS. 3 and 4, in order to adapt the lens 1 bothto near and to intermediate and distance vision.

The diffractive structure 5 generates a plurality of further focalpoints F_(i) (i= . . . , −2, −1, 1, 2 etc.) located on the optical axis4 which are distributed symmetrically around the refractive focal pointF_(r), wherein the refractive focal point F_(r) is provided by the shapeof the lens 1, irrespective of the plotted diffractive structure 5. Thediffractive focal points F₁, F₂ are described as positive first orsecond order focal points respectively of the diffractive structure 5and lie on the optical axis 4 between the lens 1 and the refractivefocal point F_(r). The diffractive focal points F⁻¹, F⁻² are describedas negative first or second order focal points respectively of thediffractive structure 5 and lie on the side of the refractive focalpoint F_(r) remote from the lens 1.

Although the (position) distribution of the focal points F_(i) issymmetrical around the refractive focal point F_(r), the intensitydistribution assigned to the respective focal points F_(i) is notintended to be symmetrical. For instance, in the case of a trifocal lensin particular three maximum intensities are intended to form, namely fordistance, intermediate and near vision. This is achieved by forming thediffractive structure 5 according to FIG. 4.

According to FIG. 4 (x-axis: squared radius r² [mm]; y-axis: profiledepth T [μm]) the diffractive structure 5 comprises a periodic profilein the radial direction r of the lens 1, plotted over the squared radiusr², which has four mutually adjacent portions 6, 7, 8, 9 per period pwhich cannot be differentiated at their junctions 10, 11, 12, 13. Thephrase “plotted over the squared radius” means, with regard toperiodicity, that the period intervals p diminish on the lens 1.

In an intraocular or contact lens, for example, the period p may lie inthe range from 0.5 mm² to 1 mm² and the profile depth T in the rangefrom 2 μm to 10 μm.

In the embodiment of FIG. 4, an arbitrary “first” portion of the profile5, here the portion 9, falls monotonically and the three furtherportions 6, 7, 8 of the profile rise monotonically. The expression“first” used herein does not relate to the order of the portions 6-9,but rather serves merely to draw a distinction from three “further”portions. The order of the portions 6-9 within a period p may thus befreely selected or defined, whereby for example each of the portions 6,7, 8, 9 may be selected as the “starting” portion and/or the “first”portion 9 does not necessarily lie at the start of the period p.

In the embodiment shown in FIG. 4, the refractive focal point F_(r) isdesigned for distance vision and the three monotonically rising furtherportions 6, 7, 8 and the monotonically falling first portion 9 result intwo positive order diffractive focal points F₁, F₂ for near andintermediate vision (see FIG. 5). Alternatively, the refractive focalpoint F_(r) may for example also be designed for near vision, to whichend three monotonically falling further portions 6, 7, 8 and onemonotonically rising first portion 9 are then used, resulting in twonegative order diffractive focal points F⁻¹, F⁻² for intermediate anddistance vision (not shown).

The further portion which does not adjoin the first portion 9, i.e. inFIG. 4 the middle further portion 7, has a steeper gradient than theother two further portions 6, 8. The term “gradient” is defined hereinas the total gradient covered by a portion 6, 7, 8, 9, i.e. as thegradient between the starting point of a portion 6, 7, 8 or 9 and theend point of the same portion 6, 7, 8 or 9.

The portions 6-9, plotted over the squared radius r², may be linear,whereby a monotonically rising portion 6, 7, 8 on the lens 1 gives riseto a flank rising quadratically with r.

According to FIG. 4, moreover, the first portion 9 and the furtherportion which does not adjoin the first portion 9, i.e. here the middlefurther portion 7, are substantially vertical, i.e. they have a gradientof +/−∞. Alternatively, these two portions 7, 9 may also each mutuallyindependently have a finite gradient (not shown).

The two further portions 6, 8 which each adjoin the first portion 9 havesubstantially the same gradient, plotted over the squared radius r². Inthe case of an intraocular or contact lens, the gradient may for examplelie in the range from 1 μm/mm² to 10 μm/mm². The two portions 6, 8 mayalso comprise mutually different gradients (not shown).

The diffractive structure 5 may either be applied to the entire surfaceof one side 2, 3 of the lens 1 or merely in a central region Z₁ or anannular region Z₂ of the lens 1, as shown in FIG. 1. Alternatively or inaddition, the structure 5 may be apodised. This means that the profiledepth T of the structure 5 decreases as the lens radius r increases.

To produce the lens 1, the diffractive structure 5 may for example beincorporated directly into a lens blank, for example by turning on alathe. The lens blank could however also merely be a processablestarting material for a 3D printer, with incorporation of the structureinto the lens blank then proceeding by 3D printing of the startingmaterial to yield the multifocal lens 1.

Alternatively, the diffractive structure 5 could initially also beincorporated as a negative into a moulded blank, for example again bymeans of a lathe or a 3D printer Then, a lens material is brought intocontact with the moulded blank in order in this way to produce themultifocal lens 1. The lens material may for example already have beenprefabricated into a lens blank, into which the structure 5 is pressedor impressed by means of the moulded blank acting as a “punch”.Alternatively, the lens material may be present in a liquid or viscousstate and be cast onto the moulded blank, for example in a mould. Thelens material is then hardened, for example by the input of light orheat.

FIG. 5 shows a comparison of the intensity profile 14 (shown by a solidline) of the lens 1 presented here with the intensity profile 15 (shownby a broken line) of a lens according to the prior art (x-axis: distanceD from the lens [mm]; y-axis: relative intensity I [1]).

The lens 1 used for this comparison with the diffractive structure 5presented herein had a period p, plotted over the squared radius r², of0.65 mm², wherein the profile depth T was 4.4 μm. The two furtherportions 6, 8 which in each case adjoined the first portion 9 had,plotted over the squared radius r², a gradient of 4.3 μm/mm².

In contrast, the comparison line relating to the prior art had aperiodic profile which within one period had four portions whichsuccessively rose, fell, rose and fell monotonically.

As is clear from the diagram of FIG. 5, the result is a similarintensity distribution profile in the region of the refractive focalpoint F_(r). It is however readily apparent from FIG. 5 that the lens 1according to the prior art had greater intensity values in the region ofthe second negative focal point F⁻² of the diffractive structure 5. Incontrast, in the case of the lens 1 presented here, non-usable, negativeorder intensities are shifted into usable positive orders, as isapparent from the markedly increased intensities of the profile 10 atthe focal points F₁ and F₂, and the markedly reduced intensity of theprofile 14 at the focal point F⁻². A more intensely coloured and highercontrast image is thus obtained for the user of the described lens 1than with lenses according to the prior art

The invention is accordingly not limited to the embodiments shown butrather comprises all variants, modifications and combinations thereofwhich fall within the scope of the appended claims.

1. A multifocal lens with a refractive focal point (F_(r)) and adiffractive structure, the structure having a periodic profile in theradial direction (r) of the lens plotted over the squared radius (r²),and the profile having four mutually adjacent portions per period whichcannot be differentiated at their junctions, the four portions includinga first portion, a second portion, a third portion and a fourth portion,wherein the first portion is adjacent to the fourth and the secondportion, and the third portion is adjacent to the second and fourthportion, wherein the first portion falls monotonically and the secondportion, the third portion, and the fourth portion each risemonotonically, or a first portion rises monotonically and the secondportion, the third portion, and the fourth portion each fallmonotonically, and wherein the third portion has a steeper gradient thanthe second portion and the fourth portion, and wherein the period (p) ofthe profile, plotted over the squared radius, amounts to 0.5 mm² to 1mm² and the profile depth (T) to 2 μm to 10 μm.
 2. The multifocal lensaccording to claim 1, wherein the first portion, the second portion, thethird portion, and the fourth portion each are linear when plotted overthe squared radius (r²).
 3. The multifocal lens according to claim 1,wherein the first portion is substantially vertical.
 4. The multifocallens according to claim 1, wherein the third portion is substantiallyvertical.
 5. The multifocal lens according to claim 1, wherein thesecond portion and the fourth portion have substantially the samegradient.
 6. The multifocal lens according to claim 1, wherein thesecond portion and the fourth portion have, plotted over the squaredradius (r²), a gradient of 1 μm/mm² to 10 μm/mm².
 7. The multifocal lensaccording to claim 1, wherein the multifocal lens is an intraocular lensor contact lens.